Soap bars for cleansing are typically prepared by saponifying or neutralizing triglyceride and free fatty acids. In this saponification process, various fats (e.g., tallow, palms and coconut oil blends) are saponified in the presence of alkali (typically NaOH) to yield alkaline salts of fatty acid (derived from the fatty acid chains forming the glyceride) and glycerol. Glycerol is then typically extracted with brine to yield dilute fatty acid soap solution containing soap and aqueous phase (e.g., 70% soap and 30% aqueous phase, especially water). The soap solution is then typically dried (e.g., to about 12% water) and the remaining mass is milled, plodded and stamped into bars. Alternatively, the soap solution can be cast into moulds, blisters etc.
Soap transparency levels vary depending on the composition and production method. Cast melt soap bars are soap bars which are typically made by casting the melted composition into moulds and letting the composition cool. Extruded soap bars are usually made by producing an extruded billet of soap and cutting it into small pieces, having a bar shape; the bars are further stamped, giving the bar its desired shape. For mass market, extrusion is more economical and yields higher amounts of processed bars per minute.
Typically, compositions that yield transparent soap bars are made using cast melt processing due to the flexibility in the process and compositions which can be used. Cast melting allows very high levels of soluble material, e.g., polyols, soluble soaps, and even non-soap detergents, to be used. Conversely, extruded soap bars compositions usually provide opaque bars. It is desirable to have extruded soaps which have higher transparency.
Generally however, particularly because of the composition required to produce a transparent soap bar (i.e., having a transparency index of at least 15%, preferably at least 16%), the production of a transparent soap bar by extrusion (e.g., forming a billet and stamping the bar) is considered extremely difficult.
When extruded translucent soap bar formulations are made of a high load of palm soap (e.g., soap produced by saponification of palm oil), typically the soap bar is opaque due to the proportion of the types of fatty acids introduced from the palm blend.
U.S. Pat. No. 6,706,675 discloses a translucent soap bar composition that includes a soap mixture, a polyalkylene glycol, at least one of glycerin and sorbitol, water and optionally, free fatty acid. The soap bar composition exhibits translucent properties; the reference defines a translucent soap as one that allows light to pass through it but, as the light may be scattered by a small proportion of crystals or insolubles, it is not possible to clearly identify objects behind the translucent soap (column 1, lines 30-34). This is not the case in the present invention in which transparent bars are produced. Furthermore, the soap bar composition includes a soap mixture, a polyalkylene glycol, at least glycerin and/or sorbitol, water and optionally free fatty acid, having 0.5 to about 5.0% of a polyethylene glycol with a molecular weight in the range of about 300 to about 800 (column 2, lines 2-4), and the soap is a blend with sodium tallowate, palm oil and palm kernel oil (column 2, lines 37-39). Such oils provide soaps with amounts of palmitic to C18 (Stearic acid) acids such that ratios range from 2.17 to 18.92; according to The Lipid Handbook, Gunstone et. al., Second Edition, herein incorporated as reference. Applicants have found that these are not desired ratios for achieving transparency in fatty acid based soap bars in which fatty acid blend comes primarily from vegetable based oils. For this reason, it is believed, the reference discloses use of a polyalkylene glycol having a relatively low molecular weight to enhance the translucent properties of the soap bar composition
(Column 3, lines 25-31). In particular, PEG 8 (column 5, lines 10 to 14) is used to improve translucency. By contrast, the subject invention utilizes a balance between palmitic and C18 (stearic acid) acids to ensure that a ratio of substantially 1 in final bar is obtained (since little or no C16 and C18 in bar is introduced except through fatty acid blends, the ratio obtained from balancing the blend practically defines the ratio in the final bar). The reference also uses fatty acid blends derived from animal source, such as tallow, which are well known in the art for the production of transparent bars, while the subject invention uses fatty acid blends derived primarily from vegetal based oils which were then balanced via addition of C18 (stearic acid) or C16 (palmitic acid) acids to provide a ratio of C18 to C16 of 1:1. In short, fatty acids derived primarily from tallow (animal based oil known for production of transparent bars) and PEG 8 appear to be required in the reference to create greater translucency; this is not the case of the present invention (see Comparative 2 for lack of results from the incorporation of PEG 8 into Comparative 1 of the present invention).
WO 9958636 (Cognis Corp.) discloses a translucent personal cleansing bar with (a) an alkyl polyglycoside corresponding to formula I: R1O(Z)a wherein R1 is a monovalent organic radical having from 8 to 10 carbon atoms, and a is a number having a value of from 1.40 to 1.55; (b) a soap component derived from a fatty acid having an iodine value from 25 to about 44; and (c) water.
WO03010273 (Unilever PLC) discloses a transparent soap bar comprising: (i) from 30 to 60% by weight of the soap bar of total fatty matter wherein from >1 to 15% by weight is the salt of 12-hydroxyCi8 (Stearic acid) acid or a precursor thereof; (ii) from 20 to 50% by weight of the soap bar of at least one polyhydric alcohol; and (iii) water.
WO12136502 (Hindustan Unilever Limited) discloses a transparent soap bar with improved transparency via addition of a fluorescer at selective levels.
Thus, previous attempts to enhance transparency in soap bars are provided by inclusion of tallow in complex compositions for extruded bars using fatty acid blends derived primarily from animal source of oils or by producing via cast melt process. Transparent bars made from fatty acid blends derived predominantly from vegetal oils (e.g., oils derived from vegetable sources) are not believed known.
Nowhere is there disclosed compositions providing transparency to the soap bar while processing the bar via extrusion using simple, but unexpected, balanced ratios of fatty acids as provided by applicants' claimed invention.
The present invention is the result of experimentation investigating the use of different fatty acids (i.e. C16 (palmitic acid) and C18 (stearic acid)) in balanced amounts as an alternative to animal oil based soaps to improve transparency properties while processing the bar via extrusion. Surprisingly, soap bars with good transparency produced by extrusion can be obtained.
The compositions of the present invention have shown to yield extruded soap bars with substantially improved transparency.